But the exertions of physiological speculators did not stop here, while they were seeking with such solicitude for the source of vitality, it is not to be supposed that such an important constituent of the body, as the blood appears to be, should escape unnoticed, nor did it. That the life was in the blood, seems an opinion long since suggested, but it was treated rather as a figurative expression until revived and introduced to notice by the distinguished authority of Harvey. After him it obtained many advocates and zealous supporters in Europe and America. The opinion is entitled to notice, and I shall consider it with that principle of liberality and respect, which I think due to all opinions proceeding from such high sources. Upon the supposition that the blood was the formative principle first existing in the nascent embryo, from the action of which the various parts of the body are evolved, it was styled the Primum Vivens. But could the blood circulate without vessels? propelled chiefly by a vis atergo, unless moving in tubes or vessels; I apprehend it could never revolve in a circle and perform by secretion, the functions so necessary to the growth and nutrition of the body. Ingenuity, put upon the stretch, has drawn in support of this visionary speculation, arguments from the coagulum of the blood assuming appearances somewhat resembling muscular contraction, “and” (we are told) “as contraction is the life of the solid, if we find any thing like it, we should call it the living principle of the blood.”――On the same foundation we may assert the vitality of jelly, which can be dissolved and coagulated again, and again, present the same appearance of contraction. This quality of blood not peculiar to itself, can be referred to physical causes alone, seeing it separates spontaneously when drawn from the body, into crassamentum and serum, we are satisfied its parts are not united by chemical solution, properly so called; but are rather mingled together and kept in intimate mixture by the continual action and agitation of the circulation, for when at rest, the different parts occupy the situation assigned them by their specific gravity, and mutually recede, from the loss of caloric, and by the attraction of aggregation. An enlightened defender of this opinion of our own country, with his mind apparently more highly imbued by speculative enquiries, than the observation or proper application of facts, endeavored to substantiate a living principle in the blood from the manner in which it is influenced by chemical agents, and has brought forward experiments which, though conducted with some address appear to have been introduced rather to quadrate with preconceived opinions, than with a spirit of impartial investigation.